The aim of this article is to describe the development and implementation of structured reporting of adnexal mass findings on pelvic ultrasound in a large integrated health care delivery system. A structured reporting system that includes standardized terminology for describing adnexal masses on ultrasound was developed by a multidisciplinary team of radiologists, gynecologists, and gynecologic oncologists on the basis of literature review and internal data. The system uses a reporting template that requires radiologists to assign abnormal adnexal masses to one of five possible categories on the basis of standardized criteria: category 0, 1, 2, or 3 for masses <10 cm, to reflect increasing concern for malignancy, and category X for masses >10 cm. Unique predefined hashtags were linked to each category to enable electronic data extraction, and a hard stop feature was installed that prevents reports from being finalized without a category designation. In 2014, after a 3-month pilot study, large-scale implementation was supported by an educational campaign consisting of web-based conferences, e-mail announcements, and local presentations. Clinical management recommendations on the basis of category and other clinical factors were provided in a separate practice resource for clinicians. Analysis of adherence revealed that 93% of the approximately 12,000 reports describing abnormal adnexal masses in 2016 included category designations. Feedback from referring providers via an anonymous survey indicated high levels of satisfaction with reports. Multidisciplinary collaboration and leveraging of technology enabled large-scale implementation of structured reporting with high levels of adherence among radiologists and improved satisfaction among referring providers.